Resistance to H-induced stress-corrosion cracking is required, in particular, in the case of steel pipes which are to be used under acid gas conditions and which, therefore, may come into contact with H.sub.2 S-containing fluids. Assuring sufficient resistance requires considerable expense in the manufacturing process. It is generally known that, in particular, the following factors of influence tend to have a positive effect on the resistance to stress-corrosion cracking:
(i) a structure of the material which is as homogeneous as possible;
(ii) the least possible segregations in the material;
(iii) high fineness of grain;
(iv) as little as possible or no strain hardening;
(v) the least possible internal stress.
Due to the negative effects of strain hardening on the resistance to stress-corrosion cracking, it is generally required for steel pipes which are to be resistant to acid gas pursuant to the pertinent technical rules, such as API-5CT or NACE MR-01-75, that after cold straining there be effected a stress relief heat treatment as a result of which the values present before the strain hardening are again obtained. Various methods can be used in order to test the resistance of steel pipes to H-induced stress-corrosion cracking.
For instance, in accordance with Method D of NACE-Standard TMO177-90, the test is carried out on prestressed specimens in aqueous H.sub.2 S-containing test solutions, in which test a specific minimum value of the critical fracture toughness K.sub.ISCC must be reached. A customary value for oil field pipes of grade C90, for instance, is ##EQU1## The required values could, to be sure, also be still obtained at corresponding expense with the traditional methods of manufacture with due consideration of the above-indicated factors of influence. Nevertheless, it is desirable further to increase the values obtainable up to now in order to be able to offer even greater certainty both in production (risk of rejects) and in the use of such pipes.